(1) Field of the Invention
This invention relates to a receiving unit, receiving method, and semiconductor device and, more particularly, to a receiving unit and method for receiving and demodulating signals sent from a base station and a semiconductor device for processing signals sent from a base station.
(2) Description of the Related Art
With the wideband code division multiple access (W-CDMA) communication system, for example, signals to be sent are spread by the use of a spreading code and then are sent. A mobile station selects optimum path timing for data it receives and performs despreading, synchronous detection, and RAKE combining. As a result, data will be obtained.
After initial synchronization, usually path timing needs to be tracked frequently with a change of channel due to, for example, movement. A mobile station therefore includes a path tracking section for monitoring the timing of a path for a receiving channel.
In addition, with the W-CDMA communication system, handover control for switching a base station with which a mobile station communicates to the optimum one at any time even during receiving data is exercised in order to always realize stable communication even during moving at a high speed. Therefore, the level (signal-to-interference ratio (SIR), for example) of received data which are sent from base stations around the one with which a mobile station is communicating now must also be monitored. As a result, despreading, synchronous detection, and level measurement must be performed not only on data from the base station with which a mobile station is communicating now but also on data from other base stations.
FIG. 8 shows a block diagram of a path tracking section and data demodulating section in a conventional receiving unit which adopts the W-CDMA communication system.
As shown in FIG. 8, a conventional receiving unit which adopts the W-CDMA communication system comprises an antenna 10, receiving circuit 11, A/D converting circuit 12, path tracking section 20, data demodulating section 30, RAKE combining circuit 40, level measuring circuit 41, and power value calculating circuit 42.
The antenna 10 acquires electronic waves sent from a base station.
The receiving circuit 11 converts the electronic waves acquired by the antenna 10 into the corresponding electrical signals.
The A/D converting circuit 12 converts the electrical signals (analog signals) output from the receiving circuit 11 into the corresponding digital signals (hereinafter referred to as “received data”) and outputs them.
The path tracking section 20 includes a correlation circuit 21, integrating circuit 22, power value calculating circuit 23, integrating circuit 24, and path selecting circuit 25. The path tracking section 20 selects a path of high power on the basis of the received signals and outputs the timing of the path to the data demodulating section 30 as path information.
The correlation circuit 21 calculates a correlation value obtained from the received data supplied from the A/D converting circuit 12 and a predetermined code, being a spreading code, and outputs it to the integrating circuit 22.
The integrating circuit 22 integrates the data output from the correlation circuit 21 by the slot and outputs the result obtained.
The power value calculating circuit 23 calculates the geometric mean of the data output from the integrating circuit 22 and outputs it.
The integrating circuit 24 integrates the output from the power value calculating circuit 23 by the frame and outputs the result obtained.
The path selecting circuit 25 monitors the data output from the integrating circuit 24, selects several paths in descending order of power value, and outputs their timing as path information.
The data demodulating section 30 includes operating sections 31-1 through 31-n, a memory 32, a synchronous detection circuit 33, and a channel estimation circuit 34. The data demodulating section 30 operates a correlation value obtained from a spreading code and received data according to path information, performs synchronous detection, and outputs the original data.
The operating section 31-1 includes a correlation circuit 31-1a and code generating circuit 31-1b. The correlation circuit 31-1a operates a correlation value obtained from received data and a spreading code supplied from the code generating circuit 31-1b with timing corresponding to path information supplied from the path selecting circuit 25 and outputs the result.
The structure of the operating sections 31-2 through 31-n is the same as that of the operating section 31-1, so descriptions of them will be omitted.
The memory 32 stores data output from the operating sections 31-1 through 31-n in predetermined areas.
The synchronous detection circuit 33 performs synchronous detection on the data stored in the memory 32 and outputs the original data.
The channel estimation circuit 34 integrates the data stored in the memory 32 by the frame and outputs the result.
The RAKE combining circuit 40 causes the time and phases of signals according to paths, which the synchronous detection circuit 33 separated by despreading and output, to match, combines the signals, and outputs the result.
The level measuring circuit 41 measures the level of the data output from the RAKE combining circuit 40.
The power value calculating circuit 42 calculates the geometric mean of the data output from the channel estimation circuit 34 and provides it to the level measuring circuit 41.
Now, the operation of the above conventional receiving unit will be described.
The antenna 10 acquires electronic waves sent from a base station and provides them to the receiving circuit 11.
The receiving circuit 11 converts the electronic waves acquired by the antenna 10 into the corresponding electrical signals and outputs them.
The A/D converting circuit 12 converts the electrical signals (analog signals) supplied from the receiving circuit 11 into the corresponding digital signals and provides them to the path tracking section 20 and data demodulating section 30.
The correlation circuit 21 calculates a correlation value obtained from the received data supplied from the A/D converting circuit 12 and a spreading code supplied from another block (not shown) which corresponds to the base station electronic waves from which are being received by the antenna 10, and outputs it.
The integrating circuit 22 integrates the data output from the correlation circuit 21 by the slot and outputs the result.
The power value calculating circuit 23 calculates the geometric mean of the data which the integrating circuit 0.22 calculated by integrating by the slot, and outputs it as data indicative of the power of the received signals.
The integrating circuit 24 integrates the data output from the power value calculating circuit 23 by the frame (a “frame” is greater than a “slot”) and outputs the result.
The path selecting circuit 25 refers to the data output from the integrating circuit 24, selects several (n, in this example) paths in descending order of power of received signal, and outputs their timing as path information.
Each of the operating sections 31-1 through 31-n in the data demodulating section 30 operates a correlation value obtained from a spreading code supplied from a code generating circuit and the received data supplied from the A/D converting circuit 12 in synchronization with timing shown by the path information supplied from the path selecting circuit 25 and outputs it.
The memory 32 stores the data output from the operating sections 31-1 through 31-n in predetermined areas.
The channel estimation circuit 34 integrates one slot of a pilot signal (reference signal), generates a signal indicative of the state of a transmission line (channel), and provides it to the synchronous detection circuit 33 and power value calculating circuit 42.
The RAKE combining circuit 40 causes the time and phases of signals according to paths, which the synchronous detection circuit 33 separated by despreading and output, to match, combines the signals, and outputs the result.
The level measuring circuit 41 measures the level of the data output from the RAKE combining circuit 40.
The power value calculating circuit 42 calculates the geometric mean of the data output from the channel estimation circuit 34 and provides it to the level measuring circuit 41.
However, the conventional receiving unit described above includes the correlation circuit 21 and correlation circuits 31-1a through 31-na, that is to say, (n+1) correlation circuits. This will lead to large-scale circuits because correlation circuits usually need a large circuit area.